Automatic dryer control circuit



Jan. 18, 1966 J. c. WORST 3,229,380

AUTOMATIC DRYER CONTROL CIRCUIT Filed March 2'7, 1963 5 Sheets-Sheet 1 IN VEN TOR.

Fl G. TOSEPH C. WORST H15 ATTORNEY Jan. 18, 1966 J. c. WORST 3,229,380

AUTOMATIC DRYER CONTROL CIRCUIT Filed March 27, 1963 3 Sheets-Sheet 2 F'IGZ INVENTOR. JOSEPH C. WORST Hi5 ATTORNEY Jan. 18, 1966 J. c. WORST 3,229,380

AUTOMATIC DRYER CONTROL CIRCUIT Filed March 27, 1963 5 Sheets-Sheet :5

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DRAIN HOT 60 F 5 4 COLD 6 5 m RIVE MOTOR 63 T\MER HEATER RELAY F" G 7 INVENTOR J SEPH C. WORST WWW His ATTORNEY United States Patent 3,229,380 AUTOMATIC DRYER CONTROL CIRGUIT Joseph C. Worst, Louisville, Ky., assignor to General Electric Company, a corporation of New York Filed Mar. 27, 1963, Ser. No. 268,344 6 Claims. (Cl. 34-45) This invention relates to domestic fabric drying machines, and more particularly to an electrical control system for use in fabric drying machines of the type having a cycle automatically terminated when the clothes are dry.

Automatic fabric drying machines frequently incorporate a device which controls the closure of a circuit enabling energization of the heaters. This device must necessarily be arranged so that the heaters may be energized until it is desired to terminate the drying operation. When it is desired to terminate the drying operation, it is conventional to provide a timed additional period of operation, either to insure that a complete drying of the clothes will have been effected or else to provide a timed cool down.

It is an object of my invention to provide a novel arrangement for controlling the device which determines the period during which the heaters may be energized in a fabric drying machine.

It is a further object of my invention to provide, by the same arrangement which provides termination of heater operation, for energization of a device which will give a predetermined additional period of operation of the machine.

In carrying out my invention, I provide a fabric dryer which has, in the usual way, a chamber for receiving fabrics to be dried together with heating means arranged to heat fabrics in the chamber. The operation of the heating means is controlled by suitable electric means which is effective, upon energization by a half wave alternating current, to enable the heating means to operate, and which prevents the heating means from operating at other times. A half-wave rectifier is connected in parallel with the electric means so as to shunt the electric means out for half of each cycle of alternating current voltage, and, in addition, a controlled rectifier is connected in parallel with the electric means and with the half wave rectifier.

The gate circuit of the controlled rectifier includes a second half wave rectifier and a resistance which decreases as fabrics in the chamber become dryer. This resistance, when high, prevents the controlled rectifier from conducting, but it causes the controlled rectifier to conduct during a substantial part of each half cycle when the resistance decreases to a predetermined value. Since the controlled rectifier is in parallel with the electric means it shunts out the electric means when it conducts in this manner. The electric means is, then, no longer energized on half wave alternating current when the controlled rectifier conducts during a substantial part of each half cycle, and the heating is consequently terminated. Suitable means is made responsive to conductivity of the controlled rectifier for preventing energization of the electric means for a predetermined period. Preferably, this takes the form of a timer which does not operate on half wave power, but which becomes operative on substantially full alternating current power when the controlled rectifier conducts, and times out the machine cycle, thereafter deenergizing all components.

The subject matter which constitutes my invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. The invention itself, however, both as to organization and method of operation together with further objects and advantages of the invention, may best be understood by reference to the 3,229,383 Patented Jan. 18, 1966 following description taken in conjunction with the accompanying drawings.

In the drawings, FIGURE 1 is a rear elevational view of a clothes drying machine, specifically in this case a combination washer-dryer (which is considered to be in the category of clothes drying machines), with the rear panel removed to illustrate details;

FIGURE 2 is a side elevational view of the machine, partly in section and with certain surfaces broken away to show details;

FIGURE 3 is a schematic electric wiring diagram showing a control system for the machine;

FIGURE 4 is a sequence control cam chart illustrating a control sequence for a machine having the control circuit of FIGURE 3;

FIGURE 5 is a curve showing the full alternating current supplied to the machine;

FIGURE 6 is a curve showing the half wave current initially supplied to the control device in FIGURE 3 and FIGURE 7 is a curve showing the passage of current through the controlled rectifier of FIGURE 3 when the fabric temperature indicates dryness.

Referring now to FIGURES 1 and 2 of the drawings for a description of a typical machine in which my invention may be provided, there i shown a combination clothes washing and drying machine wherein the operating elements of the machine are included within an outer cabinet structure having a central wrap-around section 1. Section 1 is supported on a base and toe-board assembly 2, and carries a separate top 3 on which is supported a backsplasher panel 4 which may, as shown, be mounted on posts 5. Control panel 4 is provided with appropriate control devices, generally shown at 6, which may control various types of washing and drying sequences. Access to the interior of the machine is provided by a door 7 formed in section 1, the door being mounted on concealed hinges and being opened by suitable means such as a latch control 8.

As best shown in FIGURE 2, the machine is of the non-vertical axis type, in this particular case the axis being horizontal. In other words, the machine has a clothes basket or drum 9 mounted for rotation on a generally horizontal axis within an outer enclosing tub structure 10. Drum 9 comprises a cylindrical outer wall 11 provided with a plurality of suitably spaced perforations 12 to allow air and water communication between the interior and the exterior of the drum. The rear of the drum is closed by means of a suitable wall plate 13. The drum also includes a front wall 14 which is formed so as to define an access or loading opening 15 in registry with an opening 16 in wrap-around section 1 provided for door 7. The basket is rotatably supported by shaft 17 which is mounted in an elongated bearing 18 supported from rear wall 19 of tub 10. The tub is also provided with an opening 20 aligned with openings 15 and 16 so that fabrics may be placed into and removed from the drum when door 7 is open. The door seals against a suitable gasket 21 during operation of the machine.

During operation of the machine, drum 9 is driven from an electric motor 22. The drive from the motor to the basket includes a pulley 23 which is secured to the motor shaft so as to rotate therewith and over which passes a belt 24 driving an adjustable sheave assembly 25. From the adjustable sheave assembly 25 a belt 26 drives a pulley 27 which is secured to rotate with a pulley 28 mounted on a linkage 29 secured to base 2 of the machine. A belt 30 connects pulley 28 to a pulley 31 secured on the end of a shaft 17 so that rotation of pulley 31 causes rotation of the shaft and consequently of the drum 9.

The drive arrangement provides, for a single speed of motor 22, variable speeds of rotation for the drum as controlled by the adjustable sheave assembly -25. The manner in which the adjustable sheave assembly controls the speed is conventional, and is fully described and illustrated in, for instance, Patent 2,970,464 issued on February 7, 1961 to John W. Toma, and assigned to the General Electric Company, assignee of the present invention. A relatively low speed such as, for instance, 47 r.p.m. may be provided for tumbling fabrics in the basket, while a relatively high speed on the order of 200 or 300 rpm, may be provided for centrifugally extracting water from the clothes, which is commonly done after washing and rinsing operations and prior to a heat drying operation.

To heat the clothes during the drying portion of the cycle there is provided within the machine a heater assembly including two electric heaters 32 and 33 which form together a unitary heater assembly. The heaters are adjacent the outer surface of the wall 11 of the drum so that during low speed rotation of the drum the wall is heated, the air adjacent the heaters is heated, and heat is provided directly to the clothes by radiation through the perforations 12.

Secured to tub is a resistance element 35 which is sensitive to temperature, the resistance of the element decreasing as the sensed temperature increases. There are many such types of elements commercially available, and they are generally-referred to as thermistors. Element 35 is so positioned that it is responsive to the temperature of the clothes which, in turn, reflects the dryness condition of the clothes. This results from the fact that, when the clothes are initially heated, there is a rise in temperature until the rate at which moisture is being evaporated from the clothes approximately equals the rate at which energy is being put into the clothes through heaters 32 and 33. At this point, there is, in effect, a temperature plateau, i.e., the temperature rises very slowly, until substantially all the moisture has been evaporated from the clothes, and then there is a sharp increase in the temperature. The resistance element 35 is positioned so as to be able to sense this.

Inasmuch as the invention being described is embodied in a combination washer dryer, the additional components of the machine will be briefly described for the purpose of providing a complete disclosure of an operative device. The water supply means includes connections 36 and 37 through which hot and cold water is supplied to the machine for the washing operation. A valve controlled by a solenoid 38 admits hot water to the machine, and a valve controlled by an opposed solenoid 39 admits cold water to the machine. The hot and cold water valves under the control of solenoids 38 and 39 discharge through a common outlet conduit 40 into a funnel 41 which leads through a conduit 42 to a sump 43 formed at the bottom of tub 10. The air gap provided by the funnel 41 makes is impossible for water to be siphoned from the machine and thus contaminate the incoming water supply line. A pressure actuated sensing device or water level control 44 controls both solenoids 38 and 39 to maintain the proper water level in the machine during the washing operation. Sensing device 44 is connected to the interior of tub 10 by a conduit 45.

The illustrated machine is of the type which provides cold water during the drying cycle for condensing from the circulating air the moisture extracted from the clothes. The condenser water is admitted to the machine through an additional solenoid actuated valve 46 which is energized during the drying operation so that the valve passes water at a slow rate sufficient to condense from the air the moisture vaporized from the clothes. As shown, the condenser water discharges into a conduit 47 and then passes through an appropriate air gap to a funnel 48 and a conduit 49 which connects with an opening 50 in the side of tub 10. From opening 50 the condenser Water passes into tub 10 and then flows in a thin sheet down the lower left wall 51 so as to cool a substantial portion of the area of the side wall and provide a large cool surface for condensing the moisture extracted from the clothes.

The wash and rinse water used during the washing portion of the operation, and the condenser water and the moisture extracted from the clothes during the drying operation, are discharged from the machine through the sump 43 arranged at the bottom of the tub. A suitable discharge hose 52 leads from the sump to a motor driven drain pump 53 preferably driven directly from the'motor 22, and which discharges through an outlet 54 to a valve 55 controlled by a suitable solenoid (schematically shown at 56 in FIGURE 3). Since pump 53 is continually operated, the draining of water from sump 43 is controlled by the drain valve, draining occurring continually during motor operation except when solenoid 56 is energized.

With the apparatus described, any suitable sequence derived from the basic sequence of washing, rinsing and spinning may be utilized to effect the washing operation of the cycle, and may be followed by suitable heat drying of the clothes as they are tumbled in drum 9.

Referring now to FIGURE 3, in order to provide automatically the proper sequence of operations, there is provided a sequence control means in the form of a timer motor 57 which controls a plurality of timer switches 58, 59, 60, 61, 62, 63, 64 and 65. Switches 58 to 65 are operated in a desired sequence by appropriate switch operating means driven by the timer motor, as indicated schematically by FIGURE 4. Sequence controls are well known, and several types are commercially available; the representation of FIGURES 3 and 4 is therefore purely schematic, it being understood that each of the switches 58 through 65 is usually operated through conventional means such as cams.

In the particular representation of FIGURES 3 and 4, it is to be understood that each of the switches 68 to 65 schematically shown in FIGURE 3 is closed during the periods indicated by the heavy black lines in FIGURE 4. In other words, the chart of FIGURE 4 may be regarded for the purpose of this application to be a development of the periphery of the respective switch operating cams, the heavy lines showing the cam rises. There is the further point that conventional timer motors currently available commercially must be operated on substantially full alternating current. That is, they will not operate on half wave current. As will be seen herebelow, this is an important aspect of one of the specific features of my invention.

The power connections for the machine include a pair of line conductors 66 and 67 adapted to be connected to a source of 230 volt single phase power, and a neutral conductor 68 which has a potential difference, when the machine is connected to the source of power, of volts with each of the conductors 66 and 67.

Switch 58 is connected in series with solenoid 46 in controlling relation thereto across lines 67 and 68. Similarly, switch 59 is in controlling relation to solenoid 56. Solenoids 38 and 39 are respectively controlled by switches 60 and 61 and also, of course, by the water level control 44 which, in FIGURE 3, is shown schematically. Switch 62 is in series with a suitable electrically operated device, such as a gear motor for instance, schematically shown at 69, provided for controlling the position of the sheave assembly 25 so as to provide either a drum tumbling speed or spin speed. Switch 63 controls the main drive motor 22. The timer motor itself is controlled by switch 64 in series therewith.

The last timer switch 65 is in series with a relay device 70 which controls a pair of switches 71 and 72 respec tively positioned in lines 66 and 67. Relay 70 and switch 65 are connected through a line 73 and the resistor 74 to the neutral conductor 68. In addition, a conductor 75 connects the timer motor 57 to conductor 73.

In parallel with relay 70 there are provided a pair of rectifiers 76 and 77. Rectifier 76 is a conventional half wave rectifier, i.e., it permits half of each cycle of alternating current to pass through it, thereby shunting out relay 70 during that half cycle even when switch 65 is closed. However, the relay 70 is so formed that it operates on half cycle current; therefore, when switch 65 is closed, and provided rectifier 77 does not conduct, relay 70, being shunted out only half of each cycle, is energized sufficiently to close its associated switches 71 and 72.

Rectifier 77 is a controlled rectifier, that is, it is an NPNP solid state device, of a type in substantial commercial use. This type of rectifier is non-conductive, even during the half cycle in which it normally conducts, until a predetermined voltage is applied to the gate 78 thereof. When this predetermined voltage is applied, the rectifier 77 becomes conductive and remains so until the voltage across it reaches substantially zero, that is, at the end of that half cycle. Thus, if the resistance in the circuit connecting the rectifier anode to gate 78, the circuit being generally indicated at 79, is sufficiently low, the voltage at gate 78 will be sufiiciently high to start conduction of current through the rectifier 77.

Circuit 79 includes a conventional diode half wave rectifier 80, a variable resistor 81, and the thermistor 35 previously referred to. It will thus be seen that, for a predetermined setting of the variable resistor 81, the achievement of the needed gate voltage to provide conduction by rectifier 77 will be a result of variation in the resistance of thermistor 35. This variation occurs in response to temperature changes of the clothes as previously explained.

The result of this circuitry is that there will be no conduction at all through controlled rectifier 77 as long as thermistor 35 has a resistance high enough to prevent the necessary gate voltage from being achieved. Consequently, the relay 70 will be shunted out only by rectifier 76 and will be energized on half wave power, i.e., it will be energized when switch 65 is closed.

However, when the clothes are substantially dry, thermistor 35 will have its resistance decreased to the point where the necessary voltage in phase with the voltage across rectifier 77, of course, will be supplied to gate 78 and the controlled rectifier 77 will become conductive for at least half of each half cycle in which it may conduct. This condition is shown in- FIGURE 7, for example. This conductivity of rectifier 77 further shunts out relay 70, causing the relay to receive current for only a small portion of each half cycle. In other words, since rectifier 76 shunts out relay 70 during each half cycle of a first polarity (as explained above) and control rectifier 77 now shunts out relay 70 during a substantial portion (preferably at least half) of each half cycle of the other (or second) polarity, relay 70 is energized for less than one half of each cycle. The relay is designed so as to be inoperative under these conditions and open switches 71 and 72, thereby terminating the heating operation.

In addition, when rectifier 77 is conductive in each half cycle there is a circuit completed for the timer motor, even with switch 64 open. This circuit, from the conductor 67, passes through rectifiers 76 and 77, then back through conductors 73 and 75 to the timer motor, and then to conductor 68. In this connection, resistance 74 is made sufficiently high so that the timer motor will receive sufficient power to be operated under these circumstances and so that the rectifiers are protected from carrying excessive current.

As previously explained, the timer motor is of the type which will not operate on half cycle and therefore, when rectifier 76 is conducting but rectifier 77 is not, the timer motor does not operate if switch 64 is open. However, as soon as the voltage at gate 78 becomes sufficiently high each half cycle to cause rectifier 77 to conduct for a substantial portion of that half cycle, the time motor will receive almost full cycle and this is sufficient to cause it to operate.

With the aforementioned description of the structure, FIGURES 3 and 4 will now be referred to together to show that the timer motor, by operating switches 58 through in the sequence shown, causes appropriate operations to be performed for a complete was-hing and drying cycle. Thus, typically, at the beginning of an operation switches 59, 60, 63 and 64 are closed. This causes the drum to operate, the drive motor 22 receiving power from the connection of line 68 through switch 63 to line 67. Also, solenoid 38 opens its valve to permit hot water to enter the drum until pressure sensitive switch 44 opens. The water is retained in the machine by the energization of solenoid 56 which closes the drain outlet.

At the end of the wash step, solenoid 56 is de-energized by the opening of switch '59, and this opens the valve permitting the pump to pass the water out of the machine to drain. After an appropriate period of this, as timed by motor 57, the cold water solenoid 39 is energized by the closing of switch 61 to cause cold water to be provided for a rinsing operation, and solenoid 56 is energized to close the drain valve. As before, water enters until level control 44 de-energizes the valve 39.v

After another drain provided by the de-energization of solenoid 59, both the hot and cold water solenoids are energized for a warm water rinse, and this water is also drained out. At the end of this third drain operation the gear motor 69 is energized to move the adjustable sheave assembly 25 to cause the basket speed to be increased to spin speed, the drain valve solenoid remaining de-energized to permit the pump to remove the water spun out of the clothes.

At the end of the spin operation switches 59, 60, 61 and 62, remain open for the remainder of the operation. Switches 58 and 65 close. As a result of the closing of switch 58, flow of the condenser Water starts. The drain valve solenoid, being de-energized, permits this water to be drained.

The closing of switch 65 energizes relay 70 on a half wave source of power, the other half of each wave being shunted out by rectifier 76. However, as described above, relay 70 is operable on half wave to close its associated switches 71 and 72. and therefore a heat drying operation starts. Of course, if so desired, an appropriate thermostatic element 82 may be positioned adjacent element 35, but calibrated so as to open and close at a higher temperature; this insures that an unreasonably high temperature will not be reached in the case of malfunctioning of other parts of the apparatus.

Shortly after the start of the drying operation (that is, the closing of switches 58 and 65) the timer motor switch 64 opens. As long as this switch was closed, the timer motor could be energized through its ordinary circuit. However, as soon as this switch opens, the timer motor is dependent upon the circuit including the two rectifiers 76 and 77 for energization and, as has been explained, will no operate as long as it receives only half cycle power. Consequently, the timer motor stops.

This state of affairs continues, with the clothes becoming dryer (by evaporation of moisture therefrom) until finally the clothes are dry enough that the temperature rises to an extent where the resistance of element 35 decreases substantially, and causes a sufliciently high voltage to be applied at gate 78 of controlled rectifier 77 that rectifier 77 conducts for at least half of each half cycle. When this happens, relay 70 is shunted out for three quarters or better of each full cycle rather than half of each cycle, and therefore releases its switches 71 and 72 so that they open, thereby de-energizing the heaters. By the same token, the timer motor 57 becomes energized through the circuit described above. The resistor 35 continues to have a low resistance for a period of several minutes even after the timers are shut off as a result of the thermal lag which is normal in apparatus of this type having a fairly large mass, all of which has been heated to a relatively high temperature.

As a result of the renewed operation of timer motor 57, as shown in FIGURE 4, the heater relay switch 65 is shortly thereafter opened to insure that, as the machine continues to cool, switches 71 and 72 will not be reclosed. For the same reason, switch 64 is reclosed to insure continued energization of timer motor 57 notwithstanding the cooling of the machine and the clothes therein. After this, the timer tolls a predetermined cool down period and then opens switches 58 and 63, as well as its own switch 64, to completely terminate the cycle.

It will be seen that a new and improved means controlling the drying operation is provided wherein a novel relationship of a heater control relay to a controlled rectifier is provided. Also, there is a novel relationship of these two elements together with a timer motor for tolling the end of the cycle.

It will be understood that, although a relatively simple control system has been shown for controlling the temperature within the basket during the heating operation, other more sophisticated temperature control systems are known, and these may readily be incorporated into the apparatus without affecting the operation of the structure which comprises my invention as described herein.

While in accordance with the patent statutes I have described what at present is considered to be the preferred embodiment of the invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein Without departing from the invention, and I therefore aim to cover in the appended claims all such changes and modifications as fall within the true spirit and scope of my invention.

The invention is disclosed here in connection with certain specific embodiments of the same which it is to be understood are for the purpose of illustration only, it being apparent that the parts are capable of modification within the spirit of the invention and the scope of the appended claims.

Having thus clearly shown and described the invention, what is claimed as new and desired to secure by Letters Patent is:

1. A fabric dryer comprising:

(a) a chamber for receiving fabrics to be dried;

(b) heating means arranged to heat fabrics in said dryer;

() electric means controlling operation of said heating means and effective upon energization on half Wave alternating current to cause operation of said heating means and to preclude operation of said heating means when energized on less than half wave alternating current;

(d) a half wave rectifier connected in parallel with said electric means so as to shunt said electric means out for half of each cycle of alternating current voltage;

(e) a controlled rectifier connected in parallel with said electric means and said half wave rectifier, said controlled rectifier having an anode and a gate;

(f) a circuit connecting said anode of said controlled rectifier to said gate thereof including a second half wave rectifier and a resistance which decreases as fabrics in said chamber become dryer, said resistance causing said controlled rectifier to conduct during a substantial part of the other half of each cycle when said resistance decreases to a predetermined value, said controlled rectifier shunting out said electric means when it conducts;

(g) and means responsive to conductivity of said con trolled rectifier to prevent energization of said electric means for a predetermined period.

2. A fabric dryer comprising:

(a) a chamber for receiving fabrics to be dried;

8. (b) heating means arranged to' heat fabrics in said chamber;

(c) switch means controlling operation of said heating means;

(d) a relay controlling said switch means and designed to operate on half wave alternating current;

(e) a half wave rectifier connected in parallel with said relay so as to shunt out said relay for one half of each cycle of alternating current voltage;

(f) a controlled rectifier connected in parallel with said relay and said half wave rectifier, said controlled rectifier having an anode and a gate;

(g) a circuit connecting said anode of said controlled rectifier to said gate thereof including a second half wave rectifier and a resistance which decreases as fabrics in said chamber become dryer, said resistance causing said controlled rectifier to conduct during a substantial part of the other half of each cycle when said resistance decreases to a predetermined value, said controlled rectifier shunting out said relay when it conducts;

(h) said relay being formed to drop out said switch means when said controlled rectifier conducts during a substantial part of said other half of each cycle;

(i) and means responsive to conductivity of said controlled rectifier to prevent energization of said relay for a predetermined period.

3. The apparatus defined in claim 1 wherein said means responsive to conductivity of said controlled rectifier includes a timer motor connected in series with said controlled rectifier and said half wave rectifier so as to be energized when both of said rectifiers conduct, said timer motor being inoperative on half wave energization and becoming operative when it is energized across substantially more than half wave power.

4. The apparatus defined in claim 1 wherein said resistance comprises a thermistor positioned to sense temperatures within said chamber at a point substantially removed from said heating means.

5. A fabric dryer comprising:

(a) a chamber for receiving fabrics to be dried;

(b) heating means arranged to heat fabrics in said dryer;

(0) means controlling and terminating operation of said heating means including a resistor having a resistance which decreases in response to temperature rises, said resistance being positioned to sense a temperature proportional to that of fabrics in said dryer;

(d) a first half wave rectifier;

(e) a controlled rectifier connected in parallel with said first half wave rectifier, said controlled rectifier having an anode and a gate;

(f) a circuit connecting said anode of said controlled rectifier to said gate thereof including a second half wave rectifier and said resistor, said resistor causing said controlled rectifier to conduct during a substantial part of one half of each cycle of alternating current when the resistance of said resistor decreases to a value indicating substantial dryness of the fabrics;

(g) and a timer motor connected in series with said first half wave rectifier and said controlled rectifier, said timer motor being designed not to operate on half wave energization but to operate when said controlled rectifier so conducts during a substantial part of said one half of each cycle and being effective when operated to cause termination of operation of said dryer.

6. A fabric dryer comprising:

(a) a chamber for receiving fabrics to be dried;

(b) heating means arranged to heat fabrics in said dryer;

(c) timer means operative to provide termination of a drying operation in said dryer;

(d) a first half wave rectifier connected in series with said timer means;

(e) a controlled rectifier connected in parallel with said first half Wave rectifier and in series with said timer means, said controlled rectifier having an anode and a gate;

(f) and a circuit connecting said anode of said controlled rectifier to said gate thereof including a second half wave rectifier and a resistance Which decreases as fabrics in said chamber become dryer, said resistance causing said controlled rectifier to conduct during a substantial part of one half of each cycle when said resistance decreases to a predetermined value;

(g) said timer means being designed not to operate on half wave energization but becoming operative when said controlled rectifier so conducts during a substantial part of said one half of each cycle.

References Cited by the Examiner UNITED STATES PATENTS Metzger 34-45 Engel et a1 3445 Frey et a1. 34-45 Schaeve et al 317132 Pittmann 317-148.52 Goldberg 317-148.52 Stone 3445 Robb 317--132 WILLIAM F. ODEA, Primary Examiner.

NORMAN YUDKOFF, Examiner.

15 J. E. DRUMMOND, Assistant Examiner. 

1. A FABRIC DRYER COMPRISING: (A) A CHAMBER FOR RECEIVING FABRICS TO BE DRIED; (B) HEATING MEANS ARRANGED TO HEAT FABRICS IN SAID DRYER; (C) ELECTRIC MEANS CONTROLLING OPERATION OF SAID HEATING MEANS AND EFFECTIVE UPON ENERGIZATION ON HALF WAVE ALTERNATING CURRENT TO CAUSE OPERATION OF SAID HEATING MEANS AND TO PRECLUDE OPERATION OF SAID HEATING MEANS WHEN ENERGIZED ON LESS THAN HALF WAVE ALTERNTING CURRENT; (D) A HALF WAVE RECTIFIER CONNECTED IN PARALLEL WITH SAID ELECTRIC MEANS SO AS TO SHUNT SAID ELECTRIC MEANS OUT FOR HALF OF EACH CYCLE OF ALTERNATING CURRENT VOLTAGE; (E) A CONTROLLED RECTIFIER CONNECTED IN PARALLEL WITH SAID ELECTRIC MEANS AND SAID HALF WAVE RECTIFIER, SAID CONTROLLED RECTIFIER HAVING AN ANODE AND A GATE; (F) A CIRCUIT CONNECTING SAID ANODE OF SAID CONTROLLED RECTIFIER TO SAID GATE THEREOF INCLUDING A SECOND HALF WAVE RECTIFIER AND A RESISTANCE WHICH DECREASES AS FABRICS IN SAID CHAMBER BECOME DRYER, SAID RESISTANCE CAUSING SAID CONTROLLED RECTIFIER TO CONDUCT DURING A SUBSTANTIAL PART OF THE OTHER HALF OF EACH CYCLE WHEN SAID RESISTANCE DECREASES TO A PREDETERMINED VALUE, SAID CONTROLLED RECTIFIER SHUNTING OUT SAID ELECTRIC MEANS WHEN IT CONDUCTS; (G) AND MEANS RESPONSIVE TO CONDUCTIVITY OF SAID CONTROLLED RECTIFIER TO PREVENT ENERGIZATION OF SAID ELECTRIC MEANS FOR A PREDETERMINED PERIOD. 